Such method is known from DE 198 10 005. In the known method a partial flow of heating water of a heating system is passed over a pressure relieve valve into a degassing apparatus in which, by pre-adjustment of the valve, an overpressure of 0.1 to 0.3 bar is maintained. The degassing apparatus comprises inserts for increasing the surface at which gas may be separated from the heating water. A float valve is used for removing the gas separated from the heating water out of the degassing apparatus into the atmosphere. The degassed heating water is fed back into the heating system.